patch 8.0.0988: warning from Covscan about using NULL pointer

Problem:    Warning from Covscan about using NULL pointer.
Solution:   Add extra check for NULL. (zdohnal)

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    988,
 /**/
     987,
 /**/